A Theoretical Study on the Biophysical Mechanisms by Which Tumor Treating Fields Affect Tumor Cells During Mitosis

Tumor treating induced fields: a new treatment option for patients with glioblastoma

Purpose

Currently, a range of electromagnetic therapies, including magnetic field therapy, micro-currents therapy, and tumor treating fields, are under investigation for their potential in central nervous system tumor research. Each of these electromagnetic therapies possesses distinct effects and limitations. Our focus is on overcoming these limitations by developing a novel electric field generator. This generator operates by producing alternating induced currents within the tumor area through electromagnetic induction.

Methods

Finite element analysis was employed to calculate the distribution of electric fields. Cell viability was assessed using the CCK-8 assay. Tumor volumes and weights served as indicators to evaluate the effectiveness of TTIF. The in-vivo imaging system was utilized to confirm tumor growth in the brains of mice.

Results

TTIF significantly inhibited the proliferation of U87 cells both in vitro and in vivo.

Conclusion

TTIF significantly inhibited the proliferation of U87 cells both in vitro and in vivo. Consequently, TTIF emerges as a potential treatment option for patients with progressive or metastatic GBM.

Insight into the surface discharge cold plasma efficient inactivation of Pseudomonas fluorescens in water based on exogenous reactive oxygen and nitrogen species: Synergistic mechanism and energy benefits

As well known, surface discharge cold plasma has efficient inactivation ability and a variety of RONS are main active particles for inactivation, but their synergistic mechanism is still not clear. Therefore, surface discharge cold plasma system was applied to treat Pseudomonas fluorescens to study bacterial inactivation mechanism and energy benefit. Results showed that energy efficiency was directly proportional to applied voltage and inversely proportional to initial concentration. Cold plasma treatment for 20 min was inactivated by approximately > 4-log10Pseudomonas fluorescens and application of •OH and 1O2 scavengers significantly improved survival rate. In addition, •OH and 1O2 destroyed cell membrane structure and membrane permeability, which promoted diffusion of RONS into cells and affecting energy metabolism and antioxidant capacity, leading to bacterial inactivation. Furthermore, accumulation of intracellular NO and ONOOH was related to infiltration of exogenous RNS, while accumulation of •OH, H2O2, 1O2, O2- was the result of joint action of endogenous and exogenous ROS. Transcriptome analysis revealed that different RONS of cold plasma were responsible for Pseudomonas fluorescens inactivation and related to activation of intracellular antioxidant defense system and regulation of genes expression related to amino acid metabolism and energy metabolism, which promoting cellular process, catalytic activity and other biochemical pathways.

Tumor treating fields for newly diagnosed high-grade glioma based on the criteria of 2021 WHO CNS5: A retrospective analysis of Chinese patients in a single center

BACKGROUND AND OBJECTIVE

High-grade glioma (HGG) is known to be characterized by a high degree of malignancy and a worse prognosis. The classical treatment is safe resection supplemented by radiotherapy and chemotherapy. Tumor treating fields (TTFields), an emerging physiotherapeutic modality that targets malignant solid tumors using medium-frequency, low-intensity, alternating electric fields to interfere with cell division, have been used for the treatment of new diagnosis of glioblastoma, however, their administration in HGG requires further clinical evidence. The efficacy and safety of TTFields in Chinese patients with HGG were retrospectively evaluated by us in a single center.

METHODS

We enrolled and analyzed 52 patients with newly diagnosed HGG undergoing surgery and standard chemoradiotherapy regimens from December 2019 to June 2022, and followed them until June 2023. Based on whether they used TTFields, they were divided into a TTFields group and a non-TTFields group. Progression-free survival (PFS) and overall survival (OS) were compared between the two groups.

RESULTS

There were 26 cases in the TTFields group and 26 cases in the non-TTFields group. In the TTFields group, the median PFS was 14.2 months (95% CI: 9.50-18.90), the median OS was 19.7 months (95% CI: 14.95-24.25) , the median interval from surgery to the start of treatment with TTFields was 2.47 months (95% CI: 1.47-4.13), and the median duration of treatment with TTFields was 10.6 months (95% CI: 9.57-11.63). 15 (57.69%) patients experienced an adverse event and no serious adverse event was reported. In the non-TTFields group, the median PFS was 9.57 months (95% CI: 6.23-12.91) and the median OS was 16.07 months (95% CI: 12.90-19.24). There was a statistically significant difference in PFS (p = 0.005) and OS (p = 0.007) between the two groups.

CONCLUSIONS

In this retrospective analysis, TTFields were observed to improve newly diagnosed HGG patients' median PFS and OS. Compliance was much higher than reported in clinical trials and safety remained good.

Electrodynamic interaction between tumor treating fields and microtubule electrophysiological activities

Tumor treating fields (TTFields) are a type of sinusoidal alternating current electric field that has proven effective in inhibiting the reproduction of dividing tumor cells. Despite their recognized impact, the precise biophysical mechanisms underlying the unique effects of TTFields remain unknown. Many of the previous studies predominantly attribute the inhibitory effects of TTFields to mitotic disruption, with intracellular microtubules identified as crucial targets. However, this conceptual framework lacks substantiation at the mesoscopic level. This study addresses the existing gap by constructing force models for tubulin and other key subcellular structures involved in microtubule electrophysiological activities under TTFields exposure. The primary objective is to explore whether the electric force or torque exerted by TTFields significantly influences the normal structure and activities of microtubules. Initially, we examine the potential effect on the dynamic stability of microtubule structures by calculating the electric field torque on the tubulin dimer orientation. Furthermore, given the importance of electrostatics in microtubule-associated activities, such as chromosome segregation and substance transport of kinesin during mitosis, we investigate the interaction between TTFields and these electrostatic processes. Our data show that the electrodynamic effects of TTFields are most likely too weak to disrupt normal microtubule electrophysiological activities significantly. Consequently, we posit that the observed cytoskeleton destruction in mitosis is more likely attributable to non-mechanical mechanisms.

Effects of exposure to alternating low-intensity, intermediate-frequency electric fields on the differentiation of human leukemic cell line U937

Studying the bioeffects of electric fields have been the subject of ongoing research which led to promising therapeutic effect, particularly in cancer treatment. Here, we investigated the impact of low-intensity, intermediate-frequency alternating electric fields on the differentiation of human myeloid leukemia cell line U937. The results showed a near twofold increase in differentiation of U937 cells treated for 24 h by alternating 600 kHz, 150 V/m electric fields, in comparison to their control groups. This measure was evaluated by latex bead phagocytosis assay, nitro blue tetrazolium test, and cell cycle analysis which revealed a significant shift in the number of cells from G2 +M to G0 +G1 phases. The simulation result for the intracellular field intensity showed around 50% attenuation with respect to the applied external field for our setup which ruled out masking of the applied field by the internal electric noise of the cell. Based on previous studies we postulate a possible calcium-related effect for the observed differentiation, yet the exact underlying mechanism requires further investigation. Finally, our results may offer a potential therapeutic method for leukemia in the future.

A review of tumor treating fields (TTFields): advancements in clinical applications and mechanistic insights

BACKGROUND

Tumor Treating Fields (TTFields) is a non-invasive modality for cancer treatment that utilizes a specific sinusoidal electric field ranging from 100 kHz to 300 kHz, with an intensity of 1 V/cm to 3 V/cm. Its purpose is to inhibit cancer cell proliferation and induce cell death. Despite promising outcomes from clinical trials, TTFields have received FDA approval for the treatment of glioblastoma multiforme (GBM) and malignant pleural mesothelioma (MPM). Nevertheless, global acceptance of TTFields remains limited. To enhance its clinical application in other types of cancer and gain a better understanding of its mechanisms of action, this review aims to summarize the current research status by examining existing literature on TTFields' clinical trials and mechanism studies.

CONCLUSIONS

Through this comprehensive review, we seek to stimulate novel ideas and provide physicians, patients, and researchers with a better comprehension of the development of TTFields and its potential applications in cancer treatment.

Therapeutic potential of tumor treating fields for malignant brain tumors

BACKGROUND

Malignant brain tumors are among the most threatening diseases of the central nervous system, and despite increasingly updated treatments, the prognosis has not been improved. Tumor treating fields (TTFields) are an emerging approach in cancer treatment using intermediate-frequency and low-intensity electric field and can lead to the development of novel therapeutic options.

RECENT FINDINGS

A series of biological processes induced by TTFields to exert anti-cancer effects have been identified. Recent studies have shown that TTFields can alter the bioelectrical state of macromolecules and organelles involved in cancer biology. Massive alterations in cancer cell proteomics and transcriptomics caused by TTFields were related to cell biological processes as well as multiple organelle structures and activities. This review addresses the mechanisms of TTFields and recent advances in the application of TTFields therapy in malignant brain tumors, especially in glioblastoma (GBM).

CONCLUSIONS

As a novel therapeutic strategy, TTFields have shown promising results in many clinical trials, especially in GBM, and continue to evolve. A growing number of patients with malignant brain tumors are being enrolled in ongoing clinical studies demonstrating that TTFields-based combination therapies can improve treatment outcomes.

Ion channels as molecular targets of glioblastoma electrotherapy

Therapies with weak, non-ionizing electromagnetic fields comprise FDA-approved treatments such as Tumor Treating Fields (TTFields) that are used for adjuvant therapy of glioblastoma. In vitro data and animal models suggest a variety of biological TTFields effects. In particular, effects ranging from direct tumoricidal, radio- or chemotherapy-sensitizing, metastatic spread-inhibiting, up to immunostimulation have been described. Diverse underlying molecular mechanisms, such as dielectrophoresis of cellular compounds during cytokinesis, disturbing the formation of the spindle apparatus during mitosis, and perforating the plasma membrane have been proposed. Little attention, however, has been paid to molecular structures that are predestinated to percept electromagnetic fields-the voltage sensors of voltage-gated ion channels. The present review article briefly summarizes the mode of action of voltage sensing by ion channels. Moreover, it introduces into the perception of ultra-weak electric fields by specific organs of fishes with voltage-gated ion channels as key functional units therein. Finally, this article provides an overview of the published data on modulation of ion channel function by diverse external electromagnetic field protocols. Combined, these data strongly point to a function of voltage-gated ion channels as transducers between electricity and biology and, hence, to voltage-gated ion channels as primary targets of electrotherapy.

Aurora B Kinase Inhibition by AZD1152 Concomitant with Tumor Treating Fields Is Effective in the Treatment of Cultures from Primary and Recurrent Glioblastomas

Tumor Treating Fields (TTFields) were incorporated into the treatment of glioblastoma, the most malignant brain tumor, after showing an effect on progression-free and overall survival in a phase III clinical trial. The combination of TTFields and an antimitotic drug might further improve this approach. Here, we tested the combination of TTFields with AZD1152, an Aurora B kinase inhibitor, in primary cultures of newly diagnosed (ndGBM) and recurrent glioblastoma (rGBM). AZD1152 concentration was titrated for each cell line and 5-30 nM were used alone or in addition to TTFields (1.6 V/cm RMS; 200 kHz) applied for 72 h using the inovitro™ system. Cell morphological changes were visualized by conventional and confocal laser microscopy. The cytotoxic effects were determined by cell viability assays. Primary cultures of ndGBM and rGBM varied in p53 mutational status; ploidy; EGFR expression and MGMT-promoter methylation status. Nevertheless; in all primary cultures; a significant cytotoxic effect was found following TTFields treatment alone and in all but one, a significant effect after treatment with AZD1152 alone was also observed. Moreover, in all primary cultures the combined treatment had the most pronounced cytotoxic effect in parallel with morphological changes. The combined treatment of TTFields and AZD1152 led to a significant reduction in the number of ndGBM and rGBM cells compared to each treatment alone. Further evaluation of this approach, which has to be considered as a proof of concept, is warranted, before entering into early clinical trials.

"Tumor Treating Fields" delivered via electromagnetic induction have varied effects across glioma cell lines and electric field amplitudes

Previous studies reported that alternating electric fields (EFs) in the intermediate frequency (100 - 300 kHz) and low intensity (1 - 3 V/cm) regime - termed "Tumor Treating Fields" (TTFields) - have a specific, anti-proliferative effect on glioblastoma multiforme (GBM) cells. However, the mechanism(s) of action remain(s) incompletely understood, hindering the clinical adoption of treatments based on TTFields. To advance the study of such treatment in vitro , we developed an inductive device to deliver EFs to cell cultures which improves thermal and osmolar regulation compared to prior devices. Using this inductive device, we applied continuous, 200 kHz electromagnetic fields (EMFs) with a radial EF amplitude profile spanning 0 - 6.5 V/cm to cultures of primary rat astrocytes and several human GBM cell lines - U87, U118, GSC827, and GSC923 - for a duration of 72 hours. Cell density was assessed via segmented pixel densities from GFP expression (U87, U118) or from staining (astrocytes, GSC827, GSC923). Further RNA-Seq analyses were performed on GSC827 and GSC923 cells. Treated cultures of all cell lines exhibited little to no change in proliferation at lower EF amplitudes (0 - 3 V/cm). At higher amplitudes (> 4 V/cm), different effects were observed. Apparent cell densities increased (U87), decreased (GSC827, GSC923), or showed little change (U118, astrocytes). RNA-Seq analyses on treated and untreated GSC827 and GSC923 cells revealed differentially expressed gene sets of interest, such as those related to cell cycle control. Up- and down-regulation, however, was not consistent across cell lines nor EF amplitudes. Our results indicate no consistent, anti-proliferative effect of 200 kHz EMFs across GBM cell lines and thus contradict previous in vitro findings. Rather, effects varied across different cell lines and EF amplitude regimes, highlighting the need to assess the effect(s) of TTFields and similar treatments on a per cell line basis.

Tumor Treating Fields (TTFields) Therapy Concomitant with Taxanes for Cancer Treatment

Non-small cell lung cancer, ovarian cancer, and pancreatic cancer all present with high morbidity and mortality. Systemic chemotherapies have historically been the cornerstone of standard of care (SOC) regimens for many cancers, but are associated with systemic toxicity. Multimodal treatment combinations can help improve patient outcomes; however, implementation is limited by additive toxicities and potential drug-drug interactions. As such, there is a high unmet need to develop additional therapies to enhance the efficacy of SOC treatments without increasing toxicity. Tumor Treating Fields (TTFields) are electric fields that exert physical forces to disrupt cellular processes critical for cancer cell viability and tumor progression. The therapy is locoregional and is delivered noninvasively to the tumor site via a portable medical device that consists of field generator and arrays that are placed on the patient's skin. As a noninvasive treatment modality, TTFields therapy-related adverse events mainly consist of localized skin reactions, which are manageable with effective acute and prophylactic treatments. TTFields selectively target cancer cells through a multi-mechanistic approach without affecting healthy cells and tissues. Therefore, the application of TTFields therapy concomitant with other cancer treatments may lead to enhanced efficacy, with low risk of further systemic toxicity. In this review, we explore TTFields therapy concomitant with taxanes in both preclinical and clinical settings. The summarized data suggest that TTFields therapy concomitant with taxanes may be beneficial in the treatment of certain cancers.

The Mechanisms of Action of Tumor Treating Fields

Tumor treating fields (TTFields), a new modality of cancer treatment, are electric fields transmitted transdermally to tumors. The FDA has approved TTFields for the treatment of glioblastoma multiforme and mesothelioma, and they are currently under study in many other cancer types. While antimitotic effects were the first recognized biological anticancer activity of TTFields, data have shown that tumor treating fields achieve their anticancer effects through multiple mechanisms of action. TTFields therefore have the ability to be useful for many cancer types in combination with many different treatment modalities. Here, we review the current understanding of TTFields and their mechanisms of action.

Tumor-Treating Fields in Glioblastomas: Past, Present, and Future

Simple Summary

Glioblastoma (GBM) is the most common malignant primary brain tumor. Although the standard of care, including maximal resection, concurrent radiotherapy with temozolomide (TMZ), and adjuvant TMZ, has largely improved the prognosis of these patients, the 5-year survival rate is still < 10%. Tumor-treating fields (TTFields), a noninvasive anticancer therapeutic modality, has been rising as a fourth treatment option for GBMs, as confirmed by recent milestone large-scale phase 3 randomized trials and subsequent real-world data, elongating patient overall survival from 16 months to 21 months. However, the mechanisms of antitumor efficacy, its clinical safety, and potential benefits when combined with other treatment modalities are far from completely elucidated. As an increasing number of studies have recently been published on this topic, we conducted this updated, comprehensive review to establish an objective understanding of the mechanism of action, efficacy, safety, clinical concerns, and future perspectives of TTFields.

Abstract

Tumor-treating fields (TTFields), a noninvasive and innovative therapeutic approach, has emerged as the fourth most effective treatment option for the management of glioblastomas (GBMs), the most deadly primary brain cancer. According to on recent milestone randomized trials and subsequent observational data, TTFields therapy leads to substantially prolonged patient survival and acceptable adverse events. Clinical trials are ongoing to further evaluate the safety and efficacy of TTFields in treating GBMs and its biological and radiological correlations. TTFields is administered by delivering low-intensity, intermediate-frequency, alternating electric fields to human GBM function through different mechanisms of action, including by disturbing cell mitosis, delaying DNA repair, enhancing autophagy, inhibiting cell metabolism and angiogenesis, and limiting cancer cell migration. The abilities of TTFields to strengthen intratumoral antitumor immunity, increase the permeability of the cell membrane and the blood–brain barrier, and disrupt DNA-damage-repair processes make it a promising therapy when combined with conventional treatment modalities. However, the overall acceptance of TTFields in real-world clinical practice is still low. Given that increasing studies on this promising topic have been published recently, we conducted this updated review on the past, present, and future of TTFields in GBMs.

Synergetic Effect of Tumor Treating Fields and Zinc Oxide Nanoparticles on Cell Apoptosis and Genotoxicity of Three Different Human Cancer Cell Lines

Cancer remains a leading cause of death worldwide, despite extraordinary progress. So, new cancer treatment modalities are needed. Tumor-treating fields (TTFs) use low-intensity, intermediate-frequency alternating electric fields with reported cancer anti-mitotic properties. Moreover, nanomedicine is a promising therapy option for cancer. Numerous cancer types have been treated with nanoparticles, but zinc oxide nanoparticles (ZnO NPs) exhibit biocompatibility. Here, we investigate the activity of TTFs, a sub-lethal dose of ZnO NPs, and their combination on hepatocellular carcinoma (HepG2), the colorectal cancer cell line (HT-29), and breast cancer cell lines (MCF-7). The lethal effect of different ZnO NPs concentrations was assessed by sulforhodamine B sodium salt assay (SRB). The cell death percent was determined by flow cytometer, the genotoxicity was evaluated by comet assay, and the total antioxidant capacity was chemically measured. Our results show that TTFs alone cause cell death of 14, 8, and 17% of HepG2, HT-29, and MCF-7, respectively; 10 µg/mL ZnO NPs was the sub-lethal dose according to SRB results. The combination between TTFs and sub-lethal ZnO NPs increased the cell death to 29, 20, and 33% for HepG2, HT-29, and MCF-7, respectively, without reactive oxygen species increase. Increasing NPs potency using TTFs can be a novel technique in many biomedical applications.

Planning System for the Optimization of Electric Field Delivery using Implanted Electrodes for Brain Tumor Control

BACKGROUND

The use of non-ionizing electric fields from low intensity voltage sources (<10 V) to control malignant tumor growth is showing increasing potential as a cancer treatment modality. A method of applying these low intensity electric fields using multiple implanted electrodes within or adjacent to tumor volumes has been termed as intratumoral modulation therapy (IMT).

PURPOSE

This study explores advancements in the previously established IMT optimization algorithm, and the development of a custom treatment planning system for patient specific IMT. The practicality of the treatment planning system is demonstrated by implementing the full optimization pipeline on a brain phantom with robotic electrode implantation, post-operative imaging, and treatment stimulation.

METHODS

The integrated planning pipeline in 3D Slicer begins with importing and segmenting patient magnetic resonance images (MRI) or computed tomography (CT) images. The segmentation process is manual, followed by a semi-automatic smoothing step that allows the segmented brain and tumor mesh volumes to be smoothed and simplified by applying selected filters. Electrode trajectories are planned manually on the patient MRI or CT by selecting insertion and tip coordinates for a chosen number of electrodes. The electrode tip positions, and stimulation parameters (phase shift and voltage) can then be optimized with the custom semi-automatic IMT optimization algorithm where users can select the prescription electric field, voltage amplitude limit, tissue electrical properties, nearby organs at risk, optimization parameters (electrode tip location, individual contact phase shift and voltage), desired field coverage percent, and field conformity optimization. Tables of optimization results are displayed, and the resulting electric field is visualized as a field-map superimposed on the MR or CT image, with 3D renderings of the brain, tumor, and electrodes. Optimized electrode coordinates are transferred to robotic electrode implantation software to enable planning and subsequent implantation of the electrodes at the desired trajectories.

RESULTS

An IMT treatment planning system was developed that incorporates patient specific MRI or CT, segmentation, volume smoothing, electrode trajectory planning, electrode tip location and stimulation parameter optimization, and results visualization. All previous manual pipeline steps operating on diverse software platforms were coalesced into a single semi-automated 3D Slicer based user interface. Brain phantom validation of the full system implementation was successful in pre-operative planning, robotic electrode implantation, and post-operative treatment planning to adjust stimulation parameters based on actual implant locations. Voltage measurements were obtained in the brain phantom to determine the electrical parameters of the phantom and validate the simulated electric field distribution.

CONCLUSIONS

A custom treatment planning and implantation system for IMT has been developed in this study, and validated on a phantom brain model, providing an essential step in advancing IMT technology towards future clinical safety and efficacy investigations. This article is protected by copyright. All rights reserved.

Electric-field facilitated rapid and efficient dissociation of tissues Into viable single cells

Single-Cell Analysis is a growing field that endeavors to obtain genetic profiles of individual cells. Disruption of cell-cell junctions and digestion of extracellular matrix in tissues requires tissue-specific mechanical and chemical dissociation protocols. Here, a new approach for dissociating tissues into constituent cells is described. Placing a tissue biopsy core within a liquid-filled cavity and applying an electric field between two parallel plate electrodes facilitates rapid dissociation of complex tissues into single cells. Different solution compositions, electric field strengths, and oscillation frequencies are investigated experimentally and with COMSOL Multiphysics. The method is compared with standard chemical and mechanical approaches for tissue dissociation. Treatment of tissue samples at 100 V/cm 1 kHz facilitated dissociation of 95 ± 4% of biopsy tissue sections in as little as 5 min, threefold faster than conventional chemical-mechanical techniques. The approach affords good dissociation of tissues into single cells while preserving cell viability, morphology, and cell cycle progression, suggesting utility for sample preparation of tissue specimens for direct Single-Cell Analysis.

Electroporation and Electrochemotherapy in Gynecological and Breast Cancer Treatment

Gynecological carcinomas affect an increasing number of women and are associated with poor prognosis. The gold standard treatment plan is mainly based on surgical resection and subsequent chemotherapy with cisplatin, 5-fluorouracil, anthracyclines, or taxanes. Unfortunately, this treatment is becoming less effective and is associated with many side effects that negatively affect patients’ physical and mental well-being. Electroporation based on tumor exposure to electric pulses enables reduction in cytotoxic drugs dose while increasing their effectiveness. EP-based treatment methods have received more and more interest in recent years and are the subject of a large number of scientific studies. Some of them show promising therapeutic potential without using any cytotoxic drugs or molecules already present in the human body (e.g., calcium electroporation). This literature review aims to present the fundamental mechanisms responsible for the course of EP-based therapies and the current state of knowledge in the field of their application in the treatment of gynecological neoplasms.

Evaluating the therapeutic effect of tumor treating fields (TTFields) by monitoring the impedance across TTFields electrode arrays

BACKGROUND

Tumor Treating Fields (TTFields), are a novel, non-invasive tissue ablation technology for treatment of cancer. Tissue ablation is achieved through the continuous delivery of a narrow range of electromagnetic fields across a tumor, for a period of months. TTFields are designed to affect only cells that divide and to interfere with the cell division process. The therapy is monitored with MRI imaging, performed every couple of months. Current technology is unable to assess the treatment effectiveness in real time.

METHODS

We propose that the effect of the treatment can be assessed, in real time, by continuously measuring the change in electrical impedance across the TTFields delivery electrode arrays. An in vitro anatomic skull experimental study, with brain and tumor mimics phantom tissues was conducted to confirm the potential value of the proposed monitoring system.

RESULTS

Experiments show that measuring the change in the impedance amplitude between opposite TTFields electrode arrays, at a typical TTFields treatment frequency of (200 kHz), can detect changes in the tumor radius with a sensitivity that increases with the radius of the tumor. The study shows that TTFields electrode arrays can be used to assess the effectiveness of TTFields treatment on changes in the tumor dimensions in real time, throughout the treatement. This monitoring system may become a valuable addition to the TTFields cancer treatment technology. It could provide the means to continuously assess the effectiveness of the treatment, and thereby optimize the design of the treatment protocol.

Tumor treating fields: a comprehensive overview of the underlying molecular mechanism

INTRODUCTION

As a novel treatment modality, tumor treating fields (TTFields) exert low-intensity, medium-frequency electric fields on tumor cells. TTFields' effectiveness and safety have been demonstrated clinically and in the real world for treating glioblastoma, the most common and aggressive primary central nervous system tumor. TTFields therapy has also been approved for the management of malignant mesothelioma, and clinical trials are ongoing for NSCLC, gastric cancer, pancreatic cancer, and other solid tumors.

AREAS COVERED

This article comprehensively reviews the currently described evidence of TTFields' mechanism of action. TTFields' most evident therapeutic effect is to induce cell death by disrupting mitosis. Moreover, evidence suggests at additional mechanistic complexity, such as delayed DNA repair and heightened DNA replication stress, reversible increase in cell membrane and blood-brain barrier permeability, induction of immune response, and so on.

EXPERT OPINION

TTFields therapy has been arising as the fourth anti-tumor treatment besides surgery, radiotherapy, and antineoplastic agents in recent years. However, the precise molecular mechanisms underlying the effects of TTFields are not fully understood and some concepts remain controversial. An in-depth understanding of TTFields' effects on tumor cell and tumor microenvironment would be crucial for informing research aimed at further optimizing TTFields' efficacy and developing new combination therapies for clinical applications.

Tumor-Treating Fields: A fourth modality in cancer treatment, new practice updates

Although major innovations in treatment are advancing, cancer persists as one of the leading causes of mortality. With the rising incidence of cancer and as we treat them, patients incur short term and long-term toxicities of current traditional therapies, including chemotherapy. This imposes a significant physical, emotional, and financial burden among patients, which affects their quality of life. Tumor-Treating Fields (TTFields) is a novel innovative new treatment modality that utilizes alternating electric fields at specific intermediate frequencies to diminish tumor growth by inhibiting mitosis and thus proliferation of malignant cells. The distinguishing feature of this new treatment modality is that it is noninvasive and tolerable. In fact, TTFields is currently FDA approved for the treatment of glioblastoma multiforme (GBM) as well as malignant pleural mesothelioma (MPM). Recently, TTFields have also been found to affect immunogenic cell death resulting in stronger anti-neoplastic effects. In this review, we discuss the mechanism of action of TTFields, the plethora of clinical trials being conducted in patients with GBM, pancreatic adenocarcinoma, ovarian cancer, non-small-cell-lung-cancer (NSCLC), brain metastasis from NSCLC, and MPM and toxicity profile.

Electrotherapies for Glioblastoma

Non-thermal, intermediate frequency (100-500 kHz) electrotherapies present a unique therapeutic strategy to treat malignant neoplasms. Here, pulsed electric fields (PEFs) which induce reversible or irreversible electroporation (IRE) and tumour-treating fields (TTFs) are reviewed highlighting the foundations, advances, and considerations of each method when applied to glioblastoma (GBM). Several biological aspects of GBM that contribute to treatment complexity (heterogeneity, recurrence, resistance, and blood-brain barrier(BBB)) and electrophysiological traits which are suggested to promote glioma progression are described. Particularly, the biological responses at the cellular and molecular level to specific parameters of the electrical stimuli are discussed offering ways to compare these parameters despite the lack of a universally adopted physical description. Reviewing the literature, a disconnect is found between electrotherapy techniques and how they target the biological complexities of GBM that make treatment difficult in the first place. An attempt is made to bridge the interdisciplinary gap by mapping biological characteristics to different methods of electrotherapy, suggesting important future research topics and directions in both understanding and treating GBM. To the authors' knowledge, this is the first paper that attempts an in-tandem assessment of the biological effects of different aspects of intermediate frequency electrotherapy methods, thus offering possible strategies toward GBM treatment.

Permeabilizing Cell Membranes with Electric Fields

The biological impact of exogenous, alternating electric fields (AEFs) and direct-current electric fields has a long history of study, ranging from effects on embryonic development to influences on wound healing. In this article, we focus on the application of electric fields for the treatment of cancers. In particular, we outline the clinical impact of tumor treating fields (TTFields), a form of AEFs, on the treatment of cancers such as glioblastoma and mesothelioma. We provide an overview of the standard mechanism of action of TTFields, namely, the capability for AEFs (e.g., TTFields) to disrupt the formation and segregation of the mitotic spindle in actively dividing cells. Though this standard mechanism explains a large part of TTFields' action, it is by no means complete. The standard theory does not account for exogenously applied AEFs' influence directly upon DNA nor upon their capacity to alter the functionality and permeability of cancer cell membranes. This review summarizes the current literature to provide a more comprehensive understanding of AEFs' actions on cell membranes. It gives an overview of three mechanistic models that may explain the more recent observations into AEFs' effects: the voltage-gated ion channel, bioelectrorheological, and electroporation models. Inconsistencies were noted in both effective frequency range and field strength between TTFields versus all three proposed models. We addressed these discrepancies through theoretical investigations into the inhomogeneities of electric fields on cellular membranes as a function of disease state, external microenvironment, and tissue or cellular organization. Lastly, future experimental strategies to validate these findings are outlined. Clinical benefits are inevitably forthcoming.

Clinical Potential of Nerve Input to Tumors: A Bioelectricity Perspective

We support the notion that the neural connections of the tumor microenvironment (TME) and the associated 'bioelectricity' play significant role in the pathophysiology of cancer. In several cancers, the nerve input promotes the cancer process. While straightforward surgical denervation of tumors, therefore, could improve prognosis, resulting side effects of such a procedure would be unpredictable and irreversible. On the other hand, tumor innervation can be manipulated effectively for therapeutic purposes by alternative novel approaches broadly termed "electroceuticals." In this perspective, we evaluate the clinical potential of targeting the TME first through manipulation of the nerve input itself and second by application of electric fields directly to the tumor. The former encompasses several different biophysical and biochemical approaches. These include implantable devices, nanoparticles, and electroactive polymers, as well as optogenetics and chemogenetics. As regard bioelectrical manipulation of the tumor itself, the "tumor-treating field" technique, applied to gliomas commonly in combination with chemotherapy, is evaluated. Also, as electroceuticals, drugs acting on ion channels and neurotransmitter receptors are highlighted for completeness. It is concluded, first, that electroceuticals comprise a broad range of biomedical tools. Second, such electroceuticals present significant clinical potential for exploiting the neural component of the TME as a strategy against cancer. Finally, the inherent bioelectric characteristics of tumors themselves are also amenable to complementary approaches. Collectively, these represent an evolving, dynamic field and further progress and applications can be expected to follow both conceptually and technically.

A Correlation Between Electric Fields That Target the Cell Membrane Potential and Dividing HeLa Cancer Cell Growth Inhibition

OBJECTIVE

Clinical studies show that low intensity (single V/cm), intermediate-frequency (100 kHz-300 kHz) electric fields inhibit the growth of cancer cells, while the mechanism is not yet understood. We examine the hypothesis that electric fields modify the cell membrane potential of dividing cancer cells in a way that correlates with cells growth inhibition.

METHODS

A Schwan based mathematical model calculates the changes in HeLa cells membrane potential due to single V/cm electric fields and frequencies from 0.1 to 1 MHz. An experimental study examines the effect of these electric fields on the inhibition of HeLa cells growth in an incubator.

RESULTS

The theoretical calculation shows that the effects of these electric fields on cell membrane potential decrease with an increase in frequency. The HeLa cells experiments verified the inhibitory effect of these fields on cell growth. The inhibitory effect is decreasing with an increase in frequency, in a way that is similar to the frequency dependent effect of these fields on the cell membrane potential.

CONCLUSIONS

The superposition of the theoretical results and the experimental results suggest a correlation between the effect of these fields on the cell membrane potential and inhibition of cancer cell growth. It should be emphasized that correlations do not prove causality, however, they suggest an area for future research.

SIGNIFICANCE

These findings have value for the understanding of the mechanisms of cancer cells growth inhibition with electric fields and suggest an interesting area of research on the interaction between electromagnetic fields and cancer cells.

A Novel In Vitro Device to Deliver Induced Electromagnetic Fields to Cell and Tissue Cultures

We have developed a novel, to our knowledge, in vitro instrument that can deliver intermediate-frequency (100-400 kHz), moderate-intensity (up to and exceeding 6.5 V/cm pk-pk) electric fields (EFs) to cell and tissue cultures generated using induced electromagnetic fields (EMFs) in an air-core solenoid coil. A major application of these EFs is as an emerging cancer treatment modality. In vitro studies by Novocure reported that intermediate-frequency (100-300 kHz), low-amplitude (1-3 V/cm) EFs, which they called "tumor-treating fields (TTFields)," had an antimitotic effect on glioblastoma multiforme (GBM) cells. The effect was found to increase with increasing EF amplitude. Despite continued theoretical, preclinical, and clinical study, the mechanism of action remains incompletely understood. All previous in vitro studies of "TTFields" have used attached, capacitively coupled electrodes to deliver alternating EFs to cell and tissue cultures. This contacting delivery method suffers from a poorly characterized EF profile and conductive heating that limits the duration and amplitude of the applied EFs. In contrast, our device delivers EFs with a well-characterized radial profile in a noncontacting manner, eliminating conductive heating and enabling thermally regulated EF delivery. To test and demonstrate our system, we generated continuous, 200-kHz EMF with an EF amplitude profile spanning 0-6.5 V/cm pk-pk and applied them to exemplar human thyroid cell cultures for 72 h. We observed moderate reduction in cell density (<10%) at low EF amplitudes (<4 V/cm) and a greater reduction in cell density of up to 25% at higher amplitudes (4-6.5 V/cm). Our device can be readily extended to other EF frequency and amplitude regimes. Future studies with this device should contribute to the ongoing debate about the efficacy and mechanism(s) of action of "TTFields" by better isolating the effects of EFs and providing access to previously inaccessible EF regimes.

Tumor Treating Fields: At the Crossroads Between Physics and Biology for Cancer Treatment

Despite extraordinary advances that have been achieved in the last few decades, cancer continues to represent a leading cause of mortality worldwide. Lethal cancer types ultimately become refractory to standard of care approaches; thus, novel effective treatment options are desperately needed. Tumor Treating Fields (TTFields) are an innovative non-invasive regional anti-mitotic treatment modality with minimal systemic toxicity. TTFields are low intensity (1-3 V/cm), intermediate frequency (100-300 kHz) alternating electric fields delivered to cancer cells. In patients, TTFields are applied using FDA-approved transducer arrays, orthogonally positioned on the area surrounding the tumor region, with side effects mostly limited to the skin. The precise molecular mechanism of the anti-tumor effects of TTFields is not well-understood, but preclinical research on TTFields suggests it may act during two phases of mitosis: at metaphase, by disrupting the formation of the mitotic spindle, and at cytokinesis, by dielectrophoretic dislocation of intracellular organelles leading to cell death. This review describes the mechanism of action of TTFields and provides an overview of the most important in vitro studies that investigate the disruptive effects of TTFields in different cancer cells, focusing mainly on anti-mitotic roles. Lastly, we summarize completed and ongoing TTFields clinical trials on a variety of solid tumors.